The object of the present invention is a system and method for threading a moist web in a pulp machine or the like, such as a paper or board machine, from one section to the following section.
The object of the present invention is then typically a system for threading the tail of a pulp web from the press section to the dryer of the pulp machine. In pulp, board or paper machines there may be other corresponding points where it is necessary to transfer the moist web tail from one section of the machine to the following one. In such a case, the present invention obviously also concerns systems and methods for transferring the moist web at these points.
In this description of the invention, xe2x80x9cthe web tailxe2x80x9drefers to the narrow, typically 120 mm wide, xe2x80x9cweb stripxe2x80x9d, which is cut off from the edge of the web by a cut parallel with the longitudinal direction of the track, the said strip being that part of the web which is passed first from one section of the machine, e.g. the press section, to the following section, e.g. the dryer, for example, after a web break or at the start-up of the machine. A so-called tail threading belt or the like is used for passing the web strip forward. Once the tail end of the web strip has run the desired distance through the second section of the machine, the narrow part of the web passing through the machine is allowed to broaden to normal web width.
In a typical pulp machine, the dry-matter content of the pulp web is increased in the press section to approximately 50%. After the press section, the pulp web is typically dried in an air dryer comprising several drying levels on top of each other, through which the pulp web is passed in a winding manner from the upper part of the dryer to its lower part. The length of the air dryer is typically about 20-50 m and the number of drying levels about 10-30. The length of the route-that the pulp web runs through the air dryer is thus typically approximately 500-1000 m.
At present, a pulp web is typically passed in a free transfer from the press section to the dryer. The above-mentioned narrow web strip cut off from the edge of the pulp web is used to facilitate the feeding of the moist pulp web from the press section to the dryer, the strip being typically passed through the entire dryer, before the web is allowed to broaden to its full width. In this case, the length of the web strip is also for the most part the same as that of the drying route, that is, for example approximately 500-1000 m.
A typical system for threading the moist tail of a pulp web, that is, the above-mentioned web strip, through the pulp dryer comprises a tail threading belt which forms a closed loop. The loop is typically arranged to pass through the dryer along the route of the pulp web to be dried from the point of entry of the web to the point of its exit, and once the tail of the web has been detached from the belt, to continue outside the actual dryer, from the point of exit of the web back to the point of its entry.
The tail threading belt is typically a belt folded over once, inside which fold the tail of the pulp web, that is, the web strip, is passed through the dryer. The moist tail of the pulp web is at present passed manually from the last support wire of the press section into contact with the tail threading belt. In this case, the fold of the moving tail threading belt is first opened to allow the tail of the pulp web to be placed inside the fold. When the tail of the pulp web has been placed inside the fold, the fold is closed in order to secure the tail of the pulp web inside the fold. After this the tail threading belt is passed to the dryer. The opening and closing of the belt fold usually takes place by means of opening wheels and closing pins known as such.
FIG. 1 shows a prior art system for passing a pulp web from the support wire 10 of the press section, by means of the tail threading belt 12, to the air dryer, of which only the first roll is shown in FIG. 1. The tail threading belt 12 is a belt folded over once, the fold of which is opened to bring the tail of the web inside the fold of the belt, and closed to hold the tail of the web secured to the belt while it conveys the tail of the web through the dryer. Prior to the stage shown in FIG. 1, the tail end of the moist web strip 18 has been manually brought into contact with the tail threading belt, after it has come out of the press section supported by the last support wire 10 and fallen down freely from the roll 14. FIG. 1 also shows by means of broken lines, the running of the pulp web 18xe2x80x2 in the pulp machine during normal operation.
The functioning of a closing tail threading belt is previously known, for example, from the Finnish patent publication no. 55882. In the present description, xe2x80x9ca tail threading belt or the likexe2x80x9d refers to other tail threading arrangements known as such and comprised of endless rope, chain or cord-like means in addition to the tail threading belt disclosed in the above-mentioned Finnish patent publication, in which arrangements the web strip is pressed between two or more ropes, chains or cord-like means.
When, in the case shown in FIG. 1, the tail threading belt 16 has conveyed the tail end of the moist web strip 14 through the dryer, the forming of the strip is discontinued and the web is allowed to broaden to its normal full width. The use of the tail threading belt 16 can be discontinued after this. The pulp web will then typically run in a free transfer from the press section to the dryer, as shown by the broken lines.
Thus, at present the passing of the moist tail of the pulp web from the press to the dryer requiresxe2x80x94in connection with each start-up e.g. after each interruptionxe2x80x94a person who will take the moist tail of the pulp web manually from the press section towards the dryer and place this tail in the opened gap of the fold of the tail threading belt running at a considerable speed. This type of manual feed should be eliminated, if only because of the risk of accident.
The tail of the pulp web can usually be placed manually only in machines running at slow speeds of  less than 150 m/min. At higher speeds, the risk of unsuccessful threading increases. Today, the speed of pulp machines is often as high as 160 m/min, and there is a need to run at even higher speeds exceeding 200 m/min, in future even at speeds of 300 m/min. At present, for the above-mentioned reasons relating to manual feed, the speed of the machine has to be slowed down to less than 150 m/min for the duration of the tail threading of the web, that is, the manual escorting stage, which then slows down the start-up of the machine.
Passing the web strip manually requires considerable skill. Transferring the pulp web strip freely, for example, from the press section to the dryer is not easy either, because the pulp web, which typically weighs about 500-1000 g/m2, may easily break when it is lifted freely to a relatively great height.
Nowadays, the tightening of the tail threading belt typically takes place in vertical tail threading belt tightening towers. In the tightening towers, the tail threading belt is guided to pass through a U-shaped loop, the lower part of the loop being fitted with a weight, which tightens the belt to the desired tightness. The tightening tower can usually not be fitted to the optimal point for the running of the tail threading belt at the wet end of the dryer, but instead it has to be fitted on the side of the machine, on the tending side of the machine, so that the tightening tower will not be in the way of the tender platform, which moves in front of the dryer, or the broke sail guiding the broke. At the dry end there is no need to make corresponding transfers of the tail threading belt, because the tail of the pulp web can be guided directly into the pulper chute.
In order to guide the tail threading belt into the tightening tower at the wet end of the dryer, the belt has to be moved sideways, that is, in the cross-web direction several times. The tail threading belt then has to be guided and pressed by means of different types of xe2x80x9cfingersxe2x80x9d, xe2x80x9ctriangular platesxe2x80x9d or the like in order to support the web, which is a strain on the belt. All these tail threading belt support measures tend to wear the belt when it is rotated. In addition, long free unsupported draws inside the tightening tower may cause the tail threading belt to turn inside the tower. As the speeds of pulp machines increase, these problems are aggravated and may thus limit the tail threading speed of the pulp web.
The aim of the present invention is, therefore, to achieve an improved system and method for passing the moist tail of a web into a pulp dryer or the like, in comparison to those previously known.
This means that the aim is to achieve the type of system and method for passing the moist tail of a web in a pulp dryer or the like which will enable a more rapid start-up.
A further aim is to achieve the kind of system and method in which the tail of the web can be attached to the tail threading belt automatically and safely.
The aim is then in particular to achieve a system in a pulp machine, by means of which the tail of the pulp web can be passed mechanically from the press section into/within the closing tail threading belt or the like at normal running speed, by means of which the tail of the pulp web can be conveyed over a sufficiently long distance between the press section and the tail threading belt, and by means of which it is ensured that the tail of the pulp web remains inside the closing tail threading belt also when the pulp web broadened to full track width is drawn into the dryer.
Yet another aim is to achieve a system with improved tightness adjustment of the tail threading belt.
In order to achieve the foregoing aims, the system relating to the invention for threading the moist tail of a web through a pulp dryer or the like includes characteristic features which may be summarized as follows hereinbelow.
One typical system relating to the invention for passing the moist tail of a web, that is, a web strip cut off from the moist web by a longitudinal cut, in a pulp machine, from the press section through the pulp dryer comprises, e.g.
a tail threading belt, which is formed of a belt folded over once and connected into a loop,
means for guiding the tail threading belt along the route of the moist web to be dried through the pulp dryer, from the point of entry of the web to its point of exit, and on, from the point of exit of the web to the point of its entry,
means for transferring the moist tail of a web from the press section to the tail threading belt and for securing it to the belt, the said means comprising a transfer means proper provided with means for bringing about a suction effect, for example,
a suction roll equipped with a suction sector, or
a means equipped with a suction box and a circulating escorting belt.
The transfer means may preferably be simultaneously fitted, for the duration of the tail threading,
into contact with the moist tail of the web on the surface of the last support wire running in the press section, and
into contact with the tail threading belt,
in order to detach the moist tail of the web from the surface of the support wire by means of the suction effect, and to transfer it into contact with the tail threading belt. This means that the moist tail of the web will run for a certain distance along the circumference/surface of the transfer means at the transfer stage.
The system also comprises means for opening the fold of the tail threading belt folded over once, for fitting the moist tail of the web inside the fold, and means for re-closing the fold of the tail threading belt in order to secure the tail of the web to the tail threading belt. The fold of the tail threading belt is typically opened by means of so-called opening wheels, which for the most part open the fold fully, that is, to 180xc2x0. When the moist tail of the web has been brought into contact with the tail threading belt, while the belt moves continuously forward, the belt fold is closed, for example, by guiding with the closing pins. A web tail transfer means equipped with a suction sector is fitted preferably in contact with the tail threading belt, in the area between the tail threading belt opening means and the means for re-closing the fold.
In a preferred embodiment of the invention, the transfer means provided with a suction sector comprises a suction roll provided with a suction sector, the said roll being dimensioned to correspond to the width of the narrow tail to be cut off the web, which is approximately 100-200 mm. The overall length of the suction roll, in the direction of the axis is preferably slightly greater than the width of the tail of the web, so that the axial length of the suction sector of the suction roll corresponds to the width of the tail of the web. The diameter of the suction roll is preferably about 300-350 mm.
The suction roll is fitted above the web running, for example, on the bottom felt/support wire of the last press, in cross-web direction, on that section of the web which has been cut or will be cut for tail threading. The suction roll is preferably fitted above this narrow tail of the web so that the suction sector of the suction roll comes into contact with the web at the nip between the felt and the suction roll, or immediately after it. In this case, the suction sector is preferably arranged to extend at least over a short distance on the exit side of the nip between the felt and the suction roll, in which case the suction sector will lift the tail of the web off the felt after the nip, and guide the tail forward along a track following the curvature of the suction roll. The tail of the pulp web covers a part of the circumference of the suction roll during the transfer.
In a preferred embodiment of the invention, the tail threading belt is brought close to the last press felt/support wire so that the suction roll can be fitted between the felt and the tail threading belt, in contact with both. The first nip is then formed between the felt and the suction roll, and a second nip between the suction roll and the tail threading belt. The suction roll, felt and tail threading belt are fitted in such a way with respect to each other that the suction roll in the first nip rotates in the direction of the felt, and in the second nip in the direction of the tail threading belt. In this case the suction sector of the suction roll is arranged to extend from the first nip almost up to the second nip, which means that the suction roll conveys the tail of the web detached from the felt and transferred onto the suction roll from the first nip to the second one. However, the suction sector ends preferably slightly before the second nip, so that the tail of the web on the second nip can be transferred from the suction roll to the tail threading belt.
At the second nip, that is, the nip formed by the suction roll and the tail threading belt, air can be arranged to blow on the suction roll, which facilitates the transfer of the web tail towards the tail threading belt. Air blowing to detach the tail of the web can also be achieved, if desired, by means of a separate blowpipe fitted immediately after this second nip.
According to another preferred embodiment of the invention, the tail threading belt is also arranged to run through the first nip between the suction roll and the felt, between the moist web on the suction roll and the felt. In this case the suction sector of the suction roll is arranged at the nip and to extend a short distance on from the nip in the direction of travel of the web. The suction sector sucks the tail of the web, on the nip and over a short distance after it, by means of suction taking place through the substantially air-permeable tail threading belt, bringing it into contact with the tail threading belt, at the same time detaching the tail of the web from the felt. The length of the suction sector on the circumference of the suction roll depends, among other things, on the overall geometry of the tail threading arrangement. However, the suction sector preferably continues on from the nip far enough for the tail of the web passing through to detach in a controlled manner from the felt, to run with the tail threading belt over a distance around the circumference of the suction roll, and to become attached to the tail threading belt.
If necessary, a suction box or other similar means may be arranged in conjunction with the tail threading belt, after the suction roll, by means of which suction box or the like it is ensured that the moist web tail remains attached to the tail threading belt until the belt is again closed, that is, folded over once.
The suction roll relating to the invention functions so that it takes the web tail, that is, the pulp tail end from the bottom felt of the press and transfers it to the opened tail threading belt. The pass over to the tail threading belt functions reliably, safely and rapidly.
The suction roll described above and relating to the preferred embodiment of the invention could be replaced, for example, by an escorting belt of a suitable size and passing over two rollers, such as a felt or wire loop, in which case the tail of the web detached from the support wire of the press is guided by means of the said escorting belt towards the tail threading belt. In this way the tail of the web can be detached from the felt by means of suction through the escorting belt. This means that the suction sector can be arranged in the rollers controlling the escorting belt, or in separate suction boxes or chambers fitted inside the escorting belt.
In web tail transfer taking place by means of a felt or wire loop, the moist tail of the web can be transferred over longer distances, in which case the tail threading belt does not need to be moved towards the support wire of the press section at the start of tail threading.
It is characteristic of the solution relating to the invention that it comprises equipment which is used to grip the moist web strip and to detach it, for example, from the support wire of the press section, and to take it on to a tail threading belt or the like, typically inside a belt which can be folded over once. The equipment can be arranged to function at the normal running speed of the pulp machine. When an escorting belt is used, the equipment can be arranged to convey the moist tail of the web over a desired distance inside the tail threading belt. By means of the escorting belt it can be ensured that the moist tail of the web remains on the tail threading belt until the belt has closed,
By means of the solution relating to the invention, the moist tail of the web, the web strip, to be transferred can be escorted as desired, for example, until the tail end of the web has reached the upper part of the dryer by means of the tail threading belt, passed through the first drying level of the dryer, or even until the tail end has passed through the entire dryer. By means of the apparatus relating to the invention, the moist tail of the web passing by the apparatus can thus be guided not only when the tail end of the web itself is fed into the tail threading belt, but over a considerably longer period, that is, for as long as there is a need to do so. The solution relating to the invention allows the conveyance of, for example, a 50-100 meter long, or even longer, tail/web strip in a controlled manner from the press section to the dryer.
When the tail of the web has been conveyed in a controlled manner into the dryer, the operation of the apparatus is discontinued, and the tail of the web is merely pulled by means of the tail threading belt in the usual manner until the pulp web has finally broadened to its normal track width.
In the solution relating to the invention the tightening tower can be replaced by a mainly horizontal draw, for example, a xe2x80x9ctightening carriagexe2x80x9d in a horizontal position, which is installed either above or below the dryer. There is usually space above and below a pulp dryer for arranging these narrow tail threading belt runs. Therefore, there is no need to move the tail threading belt laterally, away from its natural run, which means that there is no need for additional belt guides or pressure which cause wear to the belts. Often tail threading speeds can also be increased.
The required tightening force is obtained by means of wires, for example, on a vertical post, which can be located, for example, close to the wall of the machine room. Alternatively, the required tightening force can be created by means of a pneumatic cylinder or the like. In this case the tightness of the tail threading belt can be adjusted continuously and tightness be reduced when the belt is not running, which would be advantageous for the belt.